Photopolymerizable compositions

Details Photopolymerizable compositions Photopolymerizable compositions

2001-10-10

2003-04-29

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S101000, C522S041000, C522S042000, C522S043000, C522S046000, C522S113000, C522S114000, C522S119000, C522S120000, C522S121000, C522S122000, C522S170000, C522S181000, C522S182000, C428S413000, C428S500000

Reexamination Certificate

active

06555595

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to novel radiation-curable or photopolymerizable compositions, processes for applying and curing the compositions and articles bearing a cured coating of the compositions. More specifically, this invention pertains to radiation-curable compositions which contain, in addition to the typical components of radiation-curable compositions, a polymer derived from 3,4-epoxy-1-butene.
BACKGROUND OF THE INVENTION
Radiation curing or photopolymerization (photo-induced free radical polymerization) has become an important and useful technique for applying and curing coatings, inks and adhesives. Radiation-curable compositions typically comprise as essential components one or more radiation-curable monomers and a photoinitiator. The compositions are applied as a coating to various articles and surfaces and the monomers are polymerized to form a film by exposing the coating of the radiation-curable composition to radiation, typically ultraviolet (UV) or electron-beam radiation.
Radiation-curable compositions utilizing photo-induced, free-radical polymerization reactions are finding uses today in a wide variety of industrial processes. See, for example,
Radiation Curing Science and Technology,
S. P. Pappas, editor, Plenum Press, New York 1992, page 2. For example, radiation-curable coating compositions are a mainstay of the wood coatings industry and are widely employed as protective and decorative coatings for metals, plastics and paper, as well as for photo-curable printing inks and adhesives. The use of radiation-curable coating compositions is growing rapidly due to the inherent low energy requirements of this technology as well as the need to eliminate the use of organic solvents which are air and water pollutants. In addition, the polymers that are formed possess excellent chemical resistance and mechanical properties. Free radical polymerizations have reached reasonably large commercial usage in the past decade and are currently growing at an overall rate of approximately 15% per year. This growth is expected to continue as industry becomes more aware of the manifold benefits of UV curing and as more restrictive environmental legislation mandating lower volatile organic compound emissions is enacted.
Radiation curing presents many advantages such as high production rates, low energy requirements and low equipment costs. In addition, it is advantageous that users are able to avoid using a solvent in the formulation of coating compositions. Solvents typically lead to environmental and/or safety hazards and require additional equipment and handling steps to remove the solvent.
Current research efforts are directed primarily to three major areas: (1) the design and synthesis of new photoinitiator systems, (2) the development of novel monomers and (3) the development of additives that modify either the cure characteristics or enhance the mechanical performance of existing photopolymerizable compositions, primarily acrylate and methacrylate systems. The present invention pertains to the use of poly(3,4-epoxy-1-butene) (polyepoxybutene) as a component of novel photoinitiator systems or compositions and as a matrix modifier in photoinitiated free radical photopolymerizations.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a novel photopolymerizable coating composition comprising (i) an ethylenically-unsaturated, photopolymerizable compound or monomer; (ii) a photoinitiator; and (iii) polyepoxybutene. The polyepoxybutene is an inexpensive hydrogen donor synergist for the free radical polymerization of the ethylenically-unsaturated, photopolymerizable compound or monomer when the coating composition is exposed to UV radiation. Polyepoxybutene also may function as a chain transfer agent during the free radical polymerization and reduce the oxygen inhibition effect which is responsible for delayed and incomplete photopolymerizations when the free radical polymerization is carried out in the presence of oxygen. The oxygen inhibition effect can cause the coating to exhibit poor mechanical properties and chemical resistance, especially in thin film applications.
Another embodiment of the present invention is a coating or film comprising a polymer of an ethylenically-unsaturated, photopolymerizable compound or monomer and polyepoxybutene. The cured coating also contains a photoinitiator or photoinitiator residue. The cured coating is believed to comprise as the film-forming polymer an addition polymer derived from one or more ethylenically-unsaturated, photopolymerizable monomers having reacted therein or thereon polyepoxybutene. The coating compositions and coatings prepared therefrom may be used as protective and decorative coatings for metals, plastics, wood, and glass. They also may find use as adhesives, printing inks, electrical and electronic encapsulants.
Polyepoxybutene is a highly useful additive and matrix modifier for photoinitiated, free-radical crosslinking polymerizations. We have found that polyepoxybutene functions as a hydrogen donor together with aromatic ketones to form an efficient photoinitiating system for photopolymerization reactions. Polyepoxybutene can increase conversions in photocurable multifunctional acrylate systems due to both chain transfer and grafting effects. During photopolymerization, grafting of the ethylenically-unsaturated, photopolymerizable compound or monomer onto the backbone of polyepoxybutene takes place. Thus, polyepoxybutene becomes an integral part of the cured polymer matrix. We also have found that the polyepoxybutene present in our novel photopolymerizable coating compositions reduces oxygen inhibition effects in photoinduced free radical polymerization systems leading to lower cost curing processes through the elimination of the use of nitrogen as an inerting gas.
In addition, polyepoxybutene has other properties that make it valuable for free radical photocuring processes. Polyepoxybutene is a high molecular weight material with some film-forming characteristics. This makes it attractive for use in coating and ink formulations that require some viscoelastic properties for optimal deposition, flow and adhesion characteristics.
DETAILED DESCRIPTION
The ethylenically-unsaturated, photopolymerizable compound or monomer typically is an &agr;,&bgr;-ethylenically-unsaturated, non-air-curing, free-radical-polymerizable monomer or oligomer or mixture of monomers or oligomers. The nature of the molecule is not critical so long as it is activated towards free-radical polymerization via the double bonds when it is exposed to UV radiation in the presence of a conventional photoinitiator compound. Such unsaturated compounds include among other types, acrylic monomers, styrenic monomers, vinyl ethers, vinyl esters, vinyl imides, vinyl amides, maleates, fumarates and mixtures thereof. Preferred monomers are acrylic monomers and oligomers and maleate and fumarate monomers and oligomers of number average molecular weight less than about 4000 containing from about 1 to about 10 unsaturated groups per molecule. A particularly preferred group of acrylic monomers is represented by the structure:
wherein R
1
is selected from hydrogen, methyl and ethyl, where n is 1 to 10, preferably 1, 2 or 3, and Z is a saturated or ethylenically-unsaturated residue of an alcohol or polyol, a carboxylic acid or polycarboxylic acid, an amine or a polyamine, an epoxide or polyepoxide or an isocyanate or polyisocyanate of a number average molecular weight less than about 4000 containing a hydrocarbon, ester, amide, ether or urethane backbone. Such monomers may be obtained by reaction of acryloyl, methacryloyl or ethacryloyl chloride with an alcohol, a polyol, an amine, or a polyamine or by the reaction of acrylic acid, methacrylic acid or ethacrylic acid with an epoxide, a polyepoxide, an isocyanate, or a polyisocyanate, or by reaction of a hydroxyalkyl acrylate, methacrylate or ethacrylate with a carboxylic acid, polycarboxylic acid, an epoxide, a polyepoxide, an isocyanate, or a polyisocyanate. Such monomers include me

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